1. Field of the Invention
The present invention relates to the generation of focused, high intensity light and, particularly, to warning lights comprised of multiple, closely spaced arrays of light emitting diodes. This invention is also directed to techniques for the fabrication of directional light sources, which produce highly visible radiation and, especially, to warning lights having plural arrays of light emitting diodes which define angularly intersecting planes. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
Recent improvements in light emitting diodes (LED""s), particularly the ability of such solid state devices to generate relatively high light flux, has permitted use of LED""s in warning lights. Restated, presently available LED""s, when grouped together to form a closely spaced array and energized simultaneously and periodically have the capability of producing pulses of light which, when appropriately directed, are of sufficiently high intensity to be highly conspicuous. However, LED""s have characteristics which result in the light generated by a closely spaced array of such devices being inefficiently utilized. Specifically, LED""s inherently include an integral plastic lens which defines the radiation pattern of the device. This radiation pattern is generally conical with the maximum intensity being on-axis. LED""s are, in fact, conventionally identified by a product number which includes an angle of divergence, with respect to the axis of the integral lens of the device, where the measured light flux is one-half that which is measured on-axis.
The environment of a warning light, i.e., installation on an emergency vehicle or aircraft, imposes relatively harsh operating conditions on a light source. It has, in the past, been thought necessary to mount all of the LED""s of an array of such devices intended for use in a warning light on a single circuit board and to encapsulate the thus formed planar array to thereby produce a rugged, unitary light source assembly.
Warning lights must meet technical requirements established by government agencies, the FAA for example, which specify a light radiation pattern, including the field of illumination. These light radiation pattern specifications are stated in terms of light intensity at various angles, measured both horizontally and vertically, with respect to a horizontal axis defined by the warning light. In the past, in order to comply with most of the established specifications, it was necessary to focus the light generated by a planar array of LED""s. The requisite focusing was, at least in part, achieved through the use of a lens disposed between the LED array and the plane in which the light intensity measurements were made. Thus, the light generated by the individual LED""s was caused to pass through at least two lenses, i.e., the integral lens of each LED and a further lens positioned in front of the LED array. A lens inherently causes attenuation of the light passing therethrough. In order to compensate for this attenuation, it was previously believed necessary to either employ more LED""s in the array, thus increasing the physical size and power requirements of the warning light, or to sacrifice LED service life by increasing the excitation current to boost light output.
The present invention overcomes the above-briefly discussed and other deficiencies and disadvantages of the prior art by providing novel and improved warning lights which utilize multiple juxtapositioned arrays of closely spaced light emitting diodes. Each of the diode arrays defines a plane oriented substantially transverse to the axes of the integral lenses of the individual diodes comprising the array. In the final assembly, the arrays are closely spaced and oriented such that the planes defined thereby intersect at angles. Thus, by judicious selection of the LED""s comprising each array and the angles of intersection of the array defined planes, the radiation pattern prescribed by a specification may be satisfied without the necessity of passing the light generated by each individual LED through at least two focusing lenses.
The invention also encompasses manufacturing techniques which facilitate formation of the multiple LED arrays comprising a light source and assembly methods for establishing the appropriate relative orientation of the multiple arrays.